1. Field of Endeavor
The present invention relates to the field of turbomachines, especially to those turbomachines with large rotor diameters, such as stationary gas turbines or steam turbines, but also to jet engines. The present invention also relates to a lamellar seal around the rotating shaft of such a machine.
2. Brief Description of the Related Art
A gas turbine includes a rotor, upon which different stages with compressor blades and turbine blades are attached, and also a stator casing. The rotor is mounted at each end of the rotor shaft in bearings.
Controlling the gas flow inside the gas turbine is of paramount importance with regard to both the functionality and the efficiency of the gas turbine. Of outstanding importance in this context is the prevention of leakage flows of the operating fluid. Therefore, seals are arranged at different points along the rotor shaft in order to at least reduce an axial leakage flow of the operating fluid along the shaft. A seal close to the bearings is of particular importance in order to prevent the lubricant of the bearing being overheated as a result of the hot fluid flow.
Differentiation can be made between three technologies of customary seals: labyrinth seals, brush seals, and lamellar seals.
Labyrinth seals do not have any, or hardly any, metal-metal contact between the rotor and the stator; therefore their sealing effect is comparatively slight. However, they offer the advantage of low rotational friction and therefore offer a long service life.
Brush seals, on the other hand, have higher friction losses on account of the rubbing between the bristle ends and the rotor shaft. This results in wear which limits the service life of the seal. The brush seals, however, offer a better blocking of the axial gas flow, particularly in the case of higher axial pressure differences.
Lamellar seals, compared with the two other technologies, have the potential for significantly improving the sealing capacity. Instead of the multiplicity of thin brush wires which are used in the case of brush seals, lamellar seals use a multiplicity of thin metal lamellae in order to seal the gap between stationary and rotating turbine components. In this case, similarly small leakages are achieved as in the case of brush seals. As a result of the modified geometry of the flexible seal elements and their increased rigidity in the axial direction, lamellar seals, however, can be used in the case of significantly higher pressure differences. This allows seals with more compact dimensions to be constructed compared with the other technologies. Moreover, a suitable design of lamellae brings about the forming of advantageous hydrodynamic effects (“blow-up” effect) which is reflected in a reduced wear behavior and consequently leads to a longer service life in an order of magnitude which cannot be achieved with brush seals.
The basic design of a lamellar seal is known from EP 933567. Instead of the bristles consisting of wires with circular cross section, thin metal lamellae or metal leaves were arranged in a controlled spacing one beneath the other and at a defined angle to the radius. The lamellae, which are oriented by their surfaces essentially parallel to the axial direction, are much stiffer in the axial direction than in the circumferential direction. Therefore, the seal can withstand higher pressure differences without its capabilities for permitting radial movements being restricted in the process. Also, the wide region on the rotor, which is brushed over by the points of the lamellae, presents the opportunity of creating a hydrodynamic force during operation which can separate the lamellae points from the shaft. In this way, a minimum distance can be created and maintained so that wear, friction heat, and friction losses are kept very low.
The gap between the lamellae is a critical design parameter: it enables the occurrence of a fluid flow in order to consequently create the hydrodynamic effect; however, it should not be so large as to allow an excessive axial leakage flow.
According to the invention which is represented in WO 2006/061324, the lamellae have spacer elements for establishing the distance between successive lamellae of the lamellar seal, and the devices for positioning and retaining the lamellae include one or more laterally protruding projections on the lamellae in the region of the spacer elements. In particular, the handling of the lamellae and their assembly to form lamellae packets is further improved by the projections being asymmetrically formed with regard to a center line of the lamellae which extends in the longitudinal direction. The asymmetry can be achieved by a projection being provided only on one side. It is also conceivable, however, for provision to be made for two oppositely-disposed projections which laterally project by different distances. Furthermore, an asymmetry can be brought about by provision being made for two oppositely-disposed projections which are located at different heights, as seen in the longitudinal direction. For establishing a distance between successive lamellae in the lamellar seal, spacer elements are preferably provided; the projections in this case are arranged in the region of the spacer elements. The spacer elements can be formed as integral elements on the lamellae as regions of greater thickness, or can be formed as separate elements.
Depending upon the selected geometry for the seal and upon the diameter of the shaft which is to be sealed, the number of lamellae per seal can go into the thousands. It is inevitable that the accuracy with which these can be produced, assembled and connected follows from this, wherein a reproducible gap between each pair of lamellae is to be ensured, which is a critical factor for the successful implementation of each possible seal design. One of the basic problems during the production of a lamellar seal is simply the difficulty in assembling this multiplicity of lamellae in a predetermined configuration with the necessary low tolerances. Critical elements are above all the dimensional stability of the angle w1 (see FIG. 2) between rotor surface and lamellae axis and the narrow gap between the lamellae.
Just as critical is the joining step in which thousands of such lamellae are connected in a fixed manner to a support structure. WO 2005/095829 proposes in this context the use of an innovative soldering process for the production of lamellar seals. By the use of special soldering foil, a super-solidus soldering is realized, during which the soldering foil remains largely in a solid state and therefore no solder penetrates into the spaces, which are to be kept free, between the lamellae.
The installation problem represents a further problem for the implementation of such a seal in such a way that a lamellar sealing ring, which is constructed in one piece, cannot be slid over the shaft end to its intended position. Therefore, a lamellar seal has to be constructed in at least two pieces in order to be joined together at the place of installation to form a homogeneous sealing ring without the basic structure and the operating principle of the seal being negatively impaired or even interrupted. Up to now, this problem has still not been satisfactorily solved.